Devices for creating medicated aerosol using propellant and medication inside a canister are widely used. Although many medications for asthma are delivered by these devices, the wide range of particle size produced along with significant forward velocity results in discomfort and impaction in the patient's oropharynx. Many attempts have been made to decrease velocity and impaction by the use of "spacers". Spacers are straight tubes or bags that are attached to the aerosol device in an attempt to provide uniform particle size with reduced velocity and impaction. Collapsible bags have also been used. The current spacers are cumbersome and have not found wide-spread patient acceptance. However, clinical studies have shown spacers to be helpful in improving delivery of drugs to patients having difficulty coordinating the high velocity of the aerosol with inhalation. Increased retention of the aerosol medication has been a problem with these devices. Without spacers, the delivery of the aerosol is uncomfortable to patients because of the cooler temperature associated with the liquified propellant and medication.
U.S. Pat. No. 4,241,877 to Hughes shows a vortex generating device in FIGS. 5A, 5B, and 6, wherein a gas and a liquid pass into a flow passage together from an inlet. The mixture flows about a rod and forms vortices thereabout and enters a bore along a portion of the rod after which the mixture exits the device through a constricted bore to a semispherical diverging outlet. The liquid is partially atomized as it leaves the bore in the inlet and becomes fully atomized as it leaves the semispherical diverging outlet in a vortical gas stream. A device is also shown where a gas and liquid under pressure are supplied together through an inlet member to a transversely extending rod for formation of vortices. The vortices flow in a direction coaxial with the rod to a constricted outlet bore and to a semispherical diverging outlet. The vortices also flow along auxiliary passages toward the constricted bore portion to combine with the previously-mentioned coaxial flowing vortices.
The Hughes '877 device is suitable for relatively high mass flow rates, but would not be suitable for use with the propellant-charged canisters containing a relatively low propellant-to-medication liquid ratio. With such canisters, it is desirable to minimize the proportion of propellant in each dose and maximize the vortical action of the mixture while it flows through the transducer. Furthermore, it would be difficult and expensive to manufacture a device as indicated in the Hughes '877 patent and still provide the aerosol production capabilities required in conjunction with the propellant-charged canister.
The inhalation device and method using vortex generating technology and combining it with entrainment on demand has resulted in a device capable of producing uniform particle size, comfortable temperature and without impaction. The reduced velocity will allow patients to easily coordinate actuations of the device with inhalation of the medicine. This will increase the amount of drug delivered to the lower respiratory tract and appropriate receptor sites instead of depositing in the oropharynx.